The objective of our research is the identification, purification and characterization of the components of the rough endoplasmic reticulum (RER) responsible for the segregation of secretory proteins within the intracisternal space of the RER. The first component of the RER to be purified and characterized is signal peptidase, the enzyme responsible for removing the signal peptide from nascent presecretory proteins. We have been able to obtain substantial purification of signal peptidase and are proceeding with its characterization. We plan to initiate studies directed at the identification and purification of the other components of the segregation apparatus.